Up to now rubber latexes are widely used in for instance the carpet industry as backing for carpets as well as in the paper and board industry for coating purposes. However, the use of such rubber latexes, i.e. a dispersion of a thermoplastic rubber in an organic solvent, are undesired from an environmental point of view due to the evaporation of organic solvent and due to the fact that recycling of latexes is not possible. Hence, there is a need for suitable, environmentally friendly alternatives for rubber latexes.
U.S. Pat. No. 4,163,031 discloses a powder composition useful for coating applications comprising a blend of 25 to 90% by weight of a selectively hydrogenated block copolymer and 75 to 10% by weight of one or more aromatic melt flow modifiers which are at least partially hydrogenated to remove the aromatic character thereof. The block copolymer comprises monovinyl arene endblocks and at least partially hydrogenated conjugated diene midblock(s) and has a monovinyl arene content of from 5 to 50% by weight. The powder composition may further contain up to 8% by weight of a silicon containing adhesion promoter. U.S. Pat. No. 4,163,031 further discloses a process for preparing such powder composition comprising the subsequent steps of melt blending the components, followed by cooling, pelletizing the composition and pulverizing, e.g. by cryogenic grounding, the pellets to the desired pellet size.
U.S. Pat. No. 4,325,770 discloses a process for preparing pressure sensitive adhesive coated products, wherein a thermoplastic elastomer and a tackifying resin are separately pulverized, after which the powders thus obtained are dry-blended at ambient temperature. The powder blend thus obtained is dry coated onto the surface of a substrate and the powder coated substrate subsequently is heated, thus allowing the powder particles to melt together to form a homogeneous coating. Finally, the coating is cooled to ambient temperature.
The thermoplastic elastomer employed is an ABA type block copolymer with A being a poly(alkenyl arene) blocks and B a poly(conjugated diene) block. Pulverizing of this block copolymer takes place at temperatures below -20.degree. C., preferably below -50.degree. C.
Both U.S. patents discussed above disclose methods of preparing powders containing elastomeric block copolymers. However, none of the powders disclosed contain any plasticizer oil, as a result of which the coatings prepared from these powders are rather rigid, which makes them unsuitable for applications requiring flexible and elastic coatings or layers, such as e.g. in carpet backings, conveyor belts, bottle cap seals, underbody car coatings and rubberized textiles, fabrics, paper or board. Up to know it was generally believed that plasticizer oils could not be part of a free flowing powder composition containing an elastomeric block copolymer, since the oil would cause the individual powder particles to adhere to one another, thus making it very difficult to handle the powder. Moreover, storage of a powder already containing oil was believed to be in fact impossible. Therefore, the normal procedure was to prepare a free flowing powder of block copolymer, possibly together with some other non-tacky components, and to add the oil only at the moment the powder was to be processed, thus avoiding agglomeration problems arising during storage. Also for reasons of expected coagulation problems, simultaneously pulverizing elastomeric polymers on the one hand and plasticizing oils and/or tackifying resins on the other hand, was avoided. This is illustrated by U.S. Pat. No. 4,325,770, where block copolymer and tackifying resin are separately pulverized before being dry-blended.
On the other hand, a resin composition for cap liners of vessels was known from e.g. Japanese patent applications J04091144A, J04031254A, J03182586 and U.S. Pat. No. 5,060,818. Japanese patent application J04091144 disclosed a bottle cap liner composition, comprising
(a) 5 to 90 wt % of a hydrogenated styrene]-butadiene] block copolymer, having a melt flow rate of 20 g/10 min or less PA1 (b) 2-50 wt % of polypropylene type resin having a melt flow rate of 0.1 to 50 g/10 min 230.degree. C., 2.16 kgf) PA1 (c) 5-70 wt % of fluidising paraffin having viscosity of 50-350 cps (37.8.degree. C.), and PA1 (d) 0.01-50 wt % of polypropylene type resin grafted with unsaturated carboxylic acid or its derivative PA1 (A) 100 parts by weight of a resin mixture, consisting of 50-5 wt % of a polypropylene type resin (homo-block- or random-copolymer) (a,1) and 50-95 wt % of hydrogenated block copolymer of styrene and butadiene (a,2), and 0.1-5 parts by weight of lubricant (a,3) or PA1 (B) 100 parts by weight of a resin mixture consisting of 70-5 wt % of polypropylene type resin (a,1) (homo-, block- or random-copolymer) and 30-95 wt % of hydrogenated block copolymer of styrene and hutadiene (a,2); PA1 0.1-5 parts by weight of a lubricant and less than 10 parts by weight of a softening agent. PA1 (i) 10-60 wt % of a hydrogenated styrene/butadiene block copolymer, PA1 (ii) 10-80 wt % of a liquid paraffin, having a viscosity of 50-400 centistokes (37.8.degree. C.) PA1 (iii) 5-60 wt % of isotactic propylene resin having a melt index of 2-20 g/10 min. PA1 (a) 100 parts by weight of a block copolymer, comprising at least one poly (predominantly monovinyl aromatic hydrocarbon) block and at least one substantially hydrogenated poly(predominantly conjugated diene) block and having a monovinyl aromatic hydrocarbon content in the range of from 10 to 60% by weight, preferably 10 to 35% by weight, based on total weight of block copolymer; PA1 (b) 100 to 200 and preferably from 100 to 150, parts by weight of a plasticiser; PA1 (c) 45 to 100, preferably 50 to 85, parts by weight of a resin, which is compatible with the substantially hydrogenated poly(conjugated diene) block; and optionally PA1 (d) a dusting agent in amount of from 0 to 10% by weight and preferably 0.5 to 3% by weight, based on total weight of composition. PA1 (a) melt blending all components present in the free flowing powder composition except the dusting agent and the blowing agent, if present, followed by cooling; PA1 (b) granulating or pelletizing the composition resulting from step (a); PA1 (c) cryogenically milling the granules or pellets resulting from step (b); and PA1 (d) dry-blending the dusting agent and optionally the blowing agent with the powder resulting from step (c).
Said composition was mentioned to show high adhesiveness to caps, flexibility, heat stability and high sealing ability.
The Japanese patent application J04031254 disclosed a disk polymer composition liner, which was pressed to the inner face of the top of metal shell. The polymer composition was a mixture of a polypropylene-based resin, a hydrogenated block copolymerised elastomer, a softening material and a lubricant.
The softening agent comprised a paraffin-based naphtalene based or aromatic-based softening agent.
The metal cap was mentioned to be used in a plastic bottle, whose filling contents requires heat sterilisation and contain a gas component, such as carbonated drinks. The use of said mixture might provide the cap with moderate rigidity.
Japanese patent application J03182586 disclosed a liner composition for plastic caps, comprising
The lubricant could be selected from the groups of amides, aliphatic esters of monoalcohols or polyols and aliphatic alcohols or acids and was preferably a higher fatty acid amide or a fatty ester of monohydroxy or polyhydroxy alcohol.
Softening agents were indicated to be paraffinic, naphtenic or aromatic hydrocarbons.
U.S. Pat. No. 5,060,818 disclosed a heat resistant lined container cover, consisting of a container cover body and a liner on the internal surface of the cover body top plating. The liner was formed by a composition, containing
In particular in column 2, lines 40 f.f. of said patent there was clearly taught, that those hydrogenated styrene/butadiene block copolymers had to be used, which had a melt index smaller than 0.1 g/10 min and preferably smaller than 0.01 g/10 min, whereas ordinary hydrogenated styrene-butadiene block copolymer had a melt index of 0.1 to 10 g/10 min, and had an extreme high molecular weight. The composition was applied under softening or melting condition to the internal surface of the cover body top plating, having the top plating area and the skirt area. The composition was pressed under cooling in to mould liner shape.
However not any reference was made in these four publications to the preparation of a stable free flowing powder, which could be easily processed into a homogeneous elastic flexible sterilisable sealant layer and more in particular could be processed by applying a layer of particles into the desired shape and transform them into a continuous homogeneous layer by a short period heat irradiation.
Accordingly, it would be very advantageous from a processing and a cost perspective, if a stable and storable, free flowing powder composition would be available, which should contain an elastomeric polymer as well as a plasticising oil, and which should be easily be processed into a homogeneous flexible and elastic layer.
The present invention aims to provide such stable free flowing powder composition containing both elastomeric polymer and plasticising oil, which composition can be stored without problems. Furthermore, it is an object of the present invention to provide a free flowing powder composition, which can be suitable applied for preparing homogeneous flexible and elastic layers. Still a further object of the present invention is to provide a process for the preparation of a stable, free flowing powder composition, which process can easily be carried out and is economically attractive. Finally, it is an object of the present invention to provide a homogeneous layer obtainable from the free flowing powder composition, which layer can suitably be applied as a wide bottle or jar cap sealant.